The navigation of magnetic medical devices, such as magnet-tipped guide wires, catheters, endoscopes, or other instruments, with a movable source magnet presents several difficulties in ensuring that the movement of the medical device is as the physician expects and intends. The difficulties arise for several reasons, including the lag between the direction of the magnetic field applied by the magnet and the actual direction of the tip of the medical device, and “coning” of the tip of the medical device as it deviates from the intended plane of the turn as it turns.